1. Field of the Disclosure
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device equipped with a balance insulating member having a bottom frame and lamp sockets integrally formed on the bottom frame.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) device is being widely used due to its advantages of light weight, thin thickness, low power consumption and the like. Accordingly, the LCD device is being widely used to display images on screens of portable computers, audio/video equipment, and office automation equipment. The LCD device displays desired images on a screen by controlling optical transmittance according to image signals applied to a plurality of controlling switching devices arranged in a matrix format.
However, since the liquid crystal display device does not have a self light-emitting characteristic, a separate device for supplying light to the liquid crystal panel, called a “backlight unit,” is needed. As an optical source for emitting light, a Cold Cathode Fluorescence Lamp (CCFL) is generally used. The CCFL is a light source tube which uses a cold cathode emission phenomenon, wherein an electron is emitted when a strong electric field is applied onto a cathode surface, and is widely used because it has the advantages of having low heat generation, high luminance, long lifetime, a full color spectrum and the like. Accordingly, the liquid crystal display device using such CCFL has been equipped with a direct-type backlight unit using a plurality of CCFLs, considering a recent trend of increasing the size of the display devices.
In the direct-type backlight unit, if a plurality of CCFLs is driven in parallel by using a transformer, only some of the plurality of CCFLs would be driven due to an electric discharge characteristic of the CCFL. That is, while the CCFL has an infinite resistance value before it discharges, the CCFL has a small resistance value after it discharges due to the formation of plasma of a conductor inside a glass tube. Accordingly, the resistance value after the CCFL discharges would become more reduced than that of an initial stage, thereby increasing an amount of a current. Therefore, when the plurality of the CCFLs are driven in parallel, the current flows toward CCFLs having a smaller resistance value after the initial electrical discharge, thereby causing some of the CCFLs to be driven and others not to be driven.
In order to solve such problems, a lamp driving apparatus for a liquid crystal display device has been disclosed in which a ballast capacitor, a capacitor of equal capacitance, is attached to both electrodes of each CCFL, thereby forming an equivalent circuit which is the same as an External Electrode Fluorescent Lamp (EEFL), thus to enable a parallel-driving of the plurality of CCFLs by using one transformer. Here, the EEFL is lighted when an AC power is applied to an external electrode, i.e., an electric discharge occurs in a discharge space inside the glass tube by an electric field due to a high frequency voltage which is applied to a pair of external electrodes, and by an ultraviolet light generating due to this electric discharge, a fluorescent substance coated on an inner circumferential surface of the glass tube emits and generates a visible ray.
Description of a balance PCB where the ballast capacitor is formed will be given.
FIG. 1 is a cross-sectional view showing a construction of a direct-type liquid crystal display device according to the related art.
As shown in FIG. 1, a reflecting plate 42 is attached onto a lower cover 41 so as to reflect light from a plurality of lamps 48 serving as a light source to a front surface.
Balance PCBs 49a and 49b for coupling a plurality of CCFLs are provided at both sides of the lower cover 41. Inverter PCBs 50a and 50b for applying an AC voltage are respectively connected to the balance PCBs 49a and 49b, which will be described later.
In addition, a diffusion plate 43 for uniformly spreading light from the lamps 48 to the front surface through the reflecting plate 42, and optical sheets 44 including a prism sheet and a protective sheet for enhancing an optical function of the light transmitted through the diffusion plate 43, are disposed above the lamps 48.
With such configuration of the backlight unit, a main support (not shown) is provided so as to maintain an overall support of the liquid crystal display device. Here, the main support is formed to have a stepped portion in a certain pattern on an upper surface thereof, in consideration of a liquid crystal panel 20 to be disposed thereon.
The liquid crystal panel 20 disposed on the main support is formed by multiple unit processes. That is, the liquid crystal panel 20 may include a Thin Film Transistor (TFT) array substrate 20a having thin film transistors arranged in each unit pixel, a color filter substrate 20b having a color filter for implementing a color, and a liquid crystal injected between the two substrates.
An upper cover (not shown) is configured to surround an outer edge of the liquid crystal panel 20 as well as side surfaces of the main support, and to be coupled to the lower cover 41 through a separate coupling means (e.g., a hook, etc.).
FIG. 2 is a perspective view showing a backlight unit according to the related art, specifically, a balance PCB and an inverter PCB on a lower cover.
Referring to FIG. 2, the inverter PCBs 50a and 50b are configured to convert a DC power supplied from an external source into an AC voltage, and convert the AC voltage into an AC voltage of a high voltage. The high AC voltage is applied to the balance PCBs 49a and 49b through an output connector of the inverter PCBs 50a and 50b, controlled an integrated circuit.
And, the high AC voltage applied to the balance PCBs 49a and 49b is supplied to respective ballast capacitors 49a1 and 49b1 through conductive wires and high voltage supply pattern (or wiring) such that a uniform amount of current is introduced into each tube of a plurality of the lamps 48 (e.g., CCFL, etc.). Then, the current is introduced into the lamps 48 connected to the respective ballast capacitors 49a1 and 49b1.
In such direct-type liquid crystal display device according to the related art, the balance PCB is mounted on the lower cover so as to stably supply a current to each of the lamps. However, the lamps are fixed to the balance PCBs by soldering, thereby reducing operation efficiency and increasing a manufacturing cost.
In addition, since a high voltage for driving the lamps is applied to the balance PCBs (or wire on the balance PCBs) provided on the lower cover, a separate insulation sheet for electrically insulating the lower cover formed of a metallic material needs to be provided while maintaining a safety distance, thereby causing the increase in the manufacturing cost.
In addition, in order to assemble (or fix) the balance PCB on the lower cover, through holes are formed on the balance PCB in a manufacturing process. Here, foreign substances may be introduced into the through holes, thereby deteriorating an external appearance of the liquid crystal display device.
By having the balance PCB on the lower cover, an outer edge of a screen on which an image is not implemented, i.e., a bezel area, becomes larger, thereby being unable to appropriately meet consumer needs, which may lead to a reduced demand in the liquid crystal display device.